Those species of animals which mankind uses to obtain milk by mechanical means such as cows, sheep and goats are by their nature animals which flee from danger. They are thus equipped with a mechanism which can cause the supply of milk to be cut off directly in case of imminent danger. This phenomenon is known and feared by all dairy workers as the so-called "milk pull-up reflex". The basic prerequisites for milk removal are therefore that first of all the animal to be milked be free of fear and have a feeling of security, calm and general well-being. By accustoming the animals to the milking operation, by developing milking methods involving no direct pain, and by selecting the animals for their milking willingness and output, the cases of total milk pull-up are rare nowadays. In addition to totally blocking the milk supply, some animals also exhibit partial blockage which fluctuates within a wide range and expresses itself in an unwillingness of the animal to give milk.
Depending on the breed of animal and the selection, there are clear differences in the animal's accustomedness to milking machines. These differences are revealed in the degree to which the udder can be emptied by the mechanical milking operation. There is one single breed of milk-giving sheep, Sardinian sheep, which are known to have good milkability. The main mechanical milking in this breed amounts to between 81 and 87%, the finish milking varying between 19 and 13%. On the average, the finish milking in breeds of sheep currently milked by machine amounts to approximately 37%. It is significant in this context that the degree of milk production by machine is so inadequate, even in breeds of sheep which are considered to have been bred well (Assaf, improved Awassi sheep), that even twin lambs, which are allowed to nurse after milking, have no difficulty in obtaining that quantity of milk required for their growth. This example documents particularly well the fact that suitable stimulation is quite obviously needed to be able in fact to withdraw all milk. This fact is confirmed by a new scientific study of seven breeds of sheep. In this study, the number of animals completely milked by machine increased on the average from 49% to 76% owing to stimulation. This increase was approximately the same in all seven breeds. Moreover, according to this study, the positive effect of udder emptying by stimulation was that the increase in the quantity of milk obtained corresponded approximately to the decline in the manual finish milking.
Rapid strides in the breeding of dairy cows have been made in the past thirty years concomitant with the general introduction of the milking machine. Today there are high-performance breeds (Holstein Frisian, German Braunvieh, German Schwarzbunte, Danish Rote) and crossbreeds (Israel Frisian, brown Swiss, Braunvieh x Holstein Frisian) which can be milked very completely by machine and yield very high milk output. On the other hand, however, the classical breeds (German Fleckvieh, Swiss Braunvieh) are quite topical and widely distributed due to a number of different breeding aims (e.g. emphasis placed on meat production, lower sensitivity, lower requirements placed on the fodder). These animals also allow themselves to be milked readily, although satisfactory emptying of the udder is only possible after adequate stimulation. But even then, the high degree of udder emptying achieved in pure breeds of dairy cows is not always attained. As scientific studies have shown, however, these breeds also react quite positively as far as annual milk and fat production are concerned (in the magnitude of +10%), if adequate stimulation (lasting from 40 to 60 seconds) is performed continuously instead of the conventional preparation of the udder (lasting from 12 to 20 seconds). Good stimulation at the beginning of lactation also directly affects the growth of the mammary gland.
The animal's willingness to give milk is basically evoked by stimulation. This applies both for the natural suckling act and for mechanical milk removal. Stimulation is a very complex process. Triggered by the stimulation stimulus, nerve reflexes relax the smooth muscles of the udder, thereby allowing in particular the fine milk ducts to dilate. Moreover, the pituitary gland secretes the hormone ocytocin into the bloodstream causing a contraction of the cells of the connective tissue septa (Korbchenzellen) which surround the milk-forming alveoli. This causes the milk, which is continuously secreted into the alveoli, to be pressed out of the spongy structure of the gland (milk ejection), thus allowing it to flow into the lower cavities in the udder and be accessible to milking. The milk ejection causes the internal udder pressure to increase to approximately 30 to 60 mbar, thereby causing the teats, promoted by an increase in the blood supply, to become engorged and open the constriction between the teat cistern and the gland cistern (the annular fold or "Furstenberg'sche Venenring"). Only now is the animal ready to be milked.
Depending on the species and breed of milk-giving animals, optimum milk output is possible only by a rapid and careful removal of the milk immediately after adequate milk ejection.
The most complete possible emptying of the udder is of utmost importance for milk production because (apart from the quantity of gland tissue and its metabolic activity) the secretion rate is dependent on the space available. The internal udder pressure increases as the storage volume is increasingly filled. Since milk secretion is accomplished against this pressure, it slows down as the degree of filling of the storage volume increases. Owing to these circumstances, the opinion which is sometimes voiced to the effect that the milk which is not removed during the preceding milking operation will also be available due the next milking operation is wrong. On the contrary, this milk is lost forever. If the udder is continuously emptied incompletely over a long period of time, this will directly result in a reduction of the daily output, in a deterioration of the animal's endurance and in a reduction of the lactation time. The influence of the degree of udder emptying on milk output is revealed the best by high-grade cows, and the least by goats, since the storage volume of the gland cisterns compared to the glandular tissue is substantially higher in cows.
It can be said in general that the better the stimulation, the more quickly and more completely milk can be obtained. If stimulation is poor, the amount of milk obtained during finish milking increases together with the amount of manual work during milking. This increase in the amount of finish milking also goes hand-in-hand with an increase in udder diseases.
Stimulation can also be effected in principle by various types of stimuli, e.g. tactile, thermal, visual, acoustical and olfactory. The greatest importance is attributed in this context to the contact and pressure receptors in the teat and the teat base. These are simulated by teat massage during manual stimulation until milk ejection occurs. The milker must allow at least 45 to 60 seconds for this. In cows, this means a mathematical average of almost double the routine time the milker accords per animal compared to the case in which there is no stimulation whatsoever preceding milk removal. Practically speaking, however, the prolongation of the routine time is less because good stimulation means that the amount of finish milk will be distinctly less, thus requiring less manual work to obtain it.
The calculation from the viewpoint of economical working is especially poor in the case of sheep, particularly because only about 10 percent of the milk obtained from a cow is obtained per milking operation from sheep. Even if hand milking, which is common in the case of sheep, were abandoned entirely, the introduction of previous manual stimulation would still reduce the work productivity, which is low in any case, by 40%. Consequently, stimulation of sheep is practised nowhere nowadays.
One must realise on the other hand that the degree of udder emptying achieved without stimulation also fluctuates very markedly from one animal to another within the same herd. Drastic drops in output and udder diseases are the necessary consequence in animals which can be milked only very incompletely without stimulation. Such udder diseases are fatal as a rule in sheep. Moreover, unprejudiced economical considerations show that ultimately no rationalisation with a view to economical working can be so great as to compensate for only slight losses in milk production. Hence, from the economical point of view, there is no alternative to the most complete possible milk production, i.e. adequate stimulation, in all milk-giving animals.
Various attempts have long been made in practice to mechanise the work of stimulation. For instance, a large variety of special-purpose brushes, vibrators and massaging means are known. These devices, however, all suffer from the drawback that the milker is still bound to the animal during the entire stimulation period. Hence, these devices achieve no savings of routine time. Furthermore, such devices usually stimulate the udder itself more than the teats, although stimulating the teats is considerably more effective.
Endeavours aimed at eliminating this drawback by semi-automation at least in the milking stall have not been successful, since the requisite positioning of the apparatus involves sophisticated technology which is accident-prone in rough, routine operation. In particular, however, this solution runs contrary to the fact that the necessary restriction in the freedom of movement of the animals frequently results in the feared "pull-up" reflex and thus, in effect, accomplishes exactly the opposite of effective stimulation. Such positioning involves great difficulties in particular in the case of restless sheep.
U.S. Pat. No. 3,554,166 already reveals an udder douche which provides for an apparatus to be placed on the floor with a plurality of upwardly directed nozzles from which a warm pressurised liquid can be sprayed against the udder. The drawbacks of such a solution are high water consumption, additional expense for heating the water and also considerable hygienic difficulties as any dirt on the udder which is dissolved by the water will run down and contaminate the teats. This can be remedied only by careful subsequent manual work.
According to U.S. Pat. No. 4,034,713, a separate device for stimulation in the stall is proposed in which one means containing a plurality of holders is provided per teat. The holders resiliently abut against the teat from various sides and have on their inwardly facing sides spray nozzles from which a warm liquid can be sprayed against the teats. The afore-mentioned apparatus, however, only serves to stimulate the teat. The milker must properly position it and remove it again at the end of the stimulation phase to be able to then apply the actual milking machine to the teats. These known stimulation devices which operate independently of the actual milking machine have shown that it is scarcely possible to ensure co-ordination between the stimulation and prompt application of the milking machine under practical conditions. If an animal is only willing to give milk for a brief time before milking, then not only does the stimulation effect disappear, but it even has an auxiliary negative effect on udder emptying in some cases. This is precisely what frequently happens in practice, because the milker as a rule operates several milking machines and is occupied with routine work, in particular positioning the machine and finishing milking another animal. As the number of milking machines increases to increase the work productivity, the milker finds himself in a continuous stress situation torn between the necessity of providing adequate stimulation, of applying the milking machine at the proper time, and of completely removing the subsequent machine milking without previous blind milking. In so doing, the milker is actually forced to decide in favour of one animal to the detriment of another.
In order to free the milker both from the actual stimulation work and from the difficulty of properly co-ordinating the individual work cycles at the beginning of the milking operation, milking machines were developed in which a preliminary phase intended to stimulate the animal precedes the main milking phase.
German AS No. 1,482,320, for example, already reveals a conventional milking procedure involving a double chamber milking cup, in which an underpressure and an atmospheric pressure are alternately applied by a pulsator to the milking cup interspace during the actual milking phase, whereas a constant underpressure prevails in the interior of the teat rubber. In this known milking machine the milking operation begins with the application of the milking cups to the teats, subsequent to which a stimulation phase is carried out such that an underpressure equal to the underpressure used during the milking phase is applied in the interior of the teat rubber. The pressure in the milking cup interspace, however, is increased above atmospheric pressure during the relaxation phase so that a greater fold-in of the teat rubbers results. This is supposed to have a massaging effect on the teats. The pressure increase in the pulsator line is returned to normal again only after the alveolar milk has ejected into the cisterns. It is not stated, however, how this is determined. Since the constant milking underpressure is already applied during the stimulation phase and the pulsator pressure gives evidence of a suction phase with the same parameters as during the milking operation, normal milk removal occurs in this case as soon as the milking cups are applied.
A milking method corresponding to German AS No. 1,482,320 is known from the article by L. Czech entitled "Automation in Milk Production" on page 164 of the periodical "Deutsche Agrartechnik", Vol. 21, No. 4, April 1971. In this procedure as well, the normal underpressure is applied to the interior of the milking cup right after the milking machine is applied to the animal. The control of the pulsator pressure, however, is varied such that a superpressure of 0.5 kp/cm.sup.2 is introduced into the milking cup interspace during the relaxation cycle, while the pressure is dropped to the underpressure customarily used in the suction phase. Hence, a vigorous massaging effect acts on the teat tips during the relaxation cycle. These changed conditions are maintained during a constant period of 60 seconds before the system is switched over to normal milking operation during which the pulsator pressure merely increases during the relaxation cycle to atmospheric pressure. Since the underpressure customarily used is applied in the suction cycles during this preliminary phase as well, normal milk removal occurs in this procedure as soon as the milking cups are applied.
In accordance with German AS No. 1,956,196 a mechanical milk removal method with double chamber milking cups is known in which it has been found that after the double chamber cup has been applied to the teat, it climbs up on the teat if the cow has not been stimulated adequately. Since this can block the flow of milk completely, this known method provides for the reduction at the beginning of the milking operation both of the underpressure in the interior of the teat rubber and of the underpressure in the milking cup interspace during the suction phases in order to avoid injury to the teat and to make milk removal possible at all. A change in the underpressure in the milking cup interspace in response to the reduced underpressure in the interior of the teat rubber is effected to avoid what is termed the "ballooning" effect. Such a drop in the underpressure also occurs in particular at the conclusion of the milking operation when the flow of milk drops off. The underpressure changes in this case strictly in response to the measured flow of milk. It is also deemed expedient to lower the pulsator frequency if the measured flow of milk diminishes because this would reduce the teat massage frequency. A high massage frequency is considered disadvantageous if there is only a slight flow or no flow of milk whatsoever, since this could cause injury to the teats. On the whole, a change in the parameters occurs in the known method only in response to the measured flow of milk.
German OS No. 2,524,398 also discloses a milking procedure in which, unlike the hitherto known method according to German AS No. 1,956,196, the underpressure in the interior of the teat rubber is elevated to ensure that in fact milk is released. According to the methods known up to that time, this was apparently not always possible in animals which were very difficult to milk because the milking vacuum was too low at the beginning of the milking operation. To spare the teats, an accordingly reduced underpressure is aupplied to the pulse space at the beginning of the milking operation when no milk or only little milk is flowing. In so doing, the underpressure prevailing in the pulse space is to be dimensioned such that the inner wall of the teat rubber is no longer completely open during the suction phase so that only the tip of the teat and not the whole teat is subjected to the underpressure. Moreover, this method is also supposed to restrict considerably the reflux of milk back against the teat, as this appears to be a dangerous factor in the spread of mastitis. This approach ensures that milk will be withdrawn reliably during the beneficial underpressure stage even in the case of animals difficult to milk. The initial phase, in which the underpressure in the pulse space is reduced, then changes over to the principal milking phase in response to the flow of milk.
U.S. Pat. No. 4,011,838 already reveals a milking method in which both the underpressure in the interior of the teat rubber and in the pulse space is reduced during a stimulation phase compared to the underpressures during the principal milking operation. According to a preferred embodiment, for instance, the underpressure in the interior of the teat rubber is 33 k Pa and 27 k Pa in the pulse space, both being considered to be especially suitable for the stimulation phase. These pressures both ensure that in normal dairy cows milk will flow immediately after relaxation of the tone of the streak canal muscles, i.e. after about 5 to 15 seconds. This process is completely independent of milk ejection, i.e. the cistern milk flows even in an unstimulated cow.
Accordingly, the regulation of the milking operation and thus the switch-over from the stimulation to main milking phase occurs in response to the flow of milk, in particular when this flow exceeds a value of 0.2 kg per minute. An auxiliary measure is provided, but only in hard-to-milk cows, that the switch-over occurs after a predetermined time of 61 seconds, even if the flow of milk has not exceeded the predetermined threshold value at this time. In addition, it is also deemed expedient that the pulse frequency be reduced during the stimulation phase below the pulse frequency in the principal milking phase.
Furthermore, a milking method is known from U.S. Pat. No. 4,211,184 in which the ballooning problem, the construction of the teat base by the annular lip of the teat rubber head and the climbing of the milking cup up the teat are supposedly solved. These objects are supposed to be achieved by measuring the amount of underpressure in the head space of the teat rubber and using this as a control signal for regulating the amount of underpressure in the pulse space in the sense that, as the underpressure in the head space increases, the underpressure in the pulse space decreases so that the teat rubber is not longer fully open during the suction phase. It is also mentioned quite passing that the means is also adapted to be used for initial stimulation. If one proceeds according to the teaching recited there, the result is that when a milking cup is applied to a teat which has not yet filled with milk and is therefore not engorged, the teat will not abut as yet against the teat rubber shaft, although there is already a full milking vacuum in the teat rubber interior. Under these conditions, the milking cup will climb up the teat until the annular lip at the head of the cup gains purchase on the teat and forms a seal. If the teat is not filled, this normally occurs at the level of the annular fold ("Furstenberg'sche Venenring"). Only after the milking cup has fully climbed up the teat does the underpressure in the pulse space drop to about 17 k Pa owing to the high milking vacuum of approximately 50 k Pa in the head interior. This drop, however, does not restore the cup to its original position once it has climbed up the teat so that, as was already described in the German patent application P No. 30 01 963, the constriction of the sensitive teat base at the level of the annular fold by the annular lip of the teat rubber head exerts a pressure on the sensitive pressure receptors at the teat base which is unpleasant for the cow and which counteracts the stimulation effect. As far as this construction of the teat base is concerned, this known process is comparable to a very normal milking machine which is applied to an udder which has not yet been filled either. As far as the stimulation is concerned, however, a normal milking machine would probably even be superior to this process due to the substantially more intensive teat massage.
German OS No. 2,423,554 already disclosed a milking method as well as an apparatus in which an inadvertent opening movement of the teat rubber hose is supposed to be precluded during the milking phase by introducing a controlled valve into the respective pulsator lines leading to the pulse spaces of the milking cup, as this opening movement can cause a reflux against the teat. This results in an impact against the tip of the teat and can cause a mechanical transmission of bacteria into the interior of the teats in the cow. A control element which substantially constricts the cross section of the pulsator line leaving only a small cross section open is therefore introduced into each pulsator line at the beginning of a milking operation as long as the milk flow is still below a predetermined threshold. The result is that the underpressure in the milking cup interspace can only build up slowly during the suction phase, whereas when the switch-over from the suction phase to the relaxation phase occurs, air can flow in immediately and increase the pressure in the pulse space to atmospheric pressure almost instantaneously. Such a procedure is hardly suitable for stimulation, since very high forces are exerted on the yet unstimulated teat in which there is no milk flow, thereby leading to injuries in the teat cistern.
The afore-mentioned methods are advantageous in that the milker is no longer confronted with the difficulty of properly allotting his time. On the other hand, however, the afore-mentioned methods only show unsatisfactory results in practice compared to manual stimulation, in particular poorer udder emptying and longer milking times. These results are quite unexpectedly extremely similar in spite of the completely different interpretations of the stimulation phase.